Time delay circuit with a relay having a primary relay coil and a secondary winding in transformer relation



Oct. 27, 1964 H. B K TIME DELAY CIRCUIT WITH A RELAY HAVING A PRIMARY RELAY COIL AND A SECONDARY WINDING IN TRANSFORMER RELATION Filed Feb. 16, 1961 3 Sheets-Sheet 1 INVENTOR. HASS AN- 5- KADAH ATTORNEY Oct. 27, 1964 H. H TIME DELAY CIRCUIT WITH A RELAY HAVING A PRIMARY RELAY SECONDARY WINDING IN TRANSFORMER RELATION COIL AND A Filed Feb. 16, 1961 3 Sheets-Sheet 2 INVENTOR.

HASSAN B KADAH BY QKM M ATTORNEY Oct. 27, 1964 H. B. KADAH 3,154,725

TIME DELAY CIRCUIT WITH A RELAY HAVING A PRIMARY RELAY COIL AND A SECONDARY WINDING IN TRANSFORMER RELATION Filed Feb. 16, 1961 5 Sheets-Sheet 5 INVEN TOR. HASSAN -B RADAH ATTO RNEY United States Patent 3,154,725 TIME DELAY CIRUUIT WITH A RELAY HAVENG A PRIMARY RELAY (30H. AND A SEQUNDARY WENDEJG IN TSFURMER RELATEQN Hassan B. Kadah, 218 Candee Ave, Syracuse, NY. Filed Feb. 16, rest, Ser. No. 89,841. 4 (Ilaims. (Cl. 3117-1 32) This invention relates to magnetic relays, and a time delay electronic circuit for controlling the application of power to a load by actuation of a relay through a predetermined time cycle.

Conventional electro-magnetic relays require for their operation, a current flow over a period of time sutlicient to actuate the relay to close a relay hold in circuit. The present invention is directed to an electronic circuit for precision time delay actuation of an electro-magnetic relay in response to an exponential voltage change derived from a resistance capacitance circuit. The invention further has to do with an electronic circuit wherein the power of the signal to actuate the relay may be less than that suflicient to assure the direct actuation of a sentitive relay. The invention [is further directed to a relay circuit wherein the initial current flow in the relay coil, which may be too weak to complete relay actuaton is employed by transformer action in the relay to trigger an electronic device such as a transistor whereby the current discharge of the capacitor determining the time delay, may provide current flow for a sufiicient interval of time to "assure completion of the relay actuation, following the initial current flow. The invention further has to do with an electro magnetic relay having a secondary coil in transformer relation to the normal coil, and wherein induced voltages in the secondary coil in response to any current impulse in the relay coil intended to actuate the relay, acts to trigger a transistor or other current flow control device to assure current flow through the normal relay coil suflicient to actuate the relay. More particularly the invention is directed to a relay, the actuation of which is desired after a fixed time delay as determined by the exponential change of voltage due to the charge or discharge of a capacitance, and wherein by simultaneous triggering, through a secondary coil in the relay, current flow to the relay coil continues following initial relay energization to assure relay operation.

The above and other novel features of the invention will appear more fully hereinafter from the following detailed description when taken in conjunction with the accompanying drawings. It is expressly understood that the drawings are employed for purposes of (illustration only and are not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawings wherein like reference characters indicate like parts:

FIGURE 1 is a circuit diagram for actuating a magnetic relay after a predetermined time delay employing a transistor having a common base and common emitter connection.

FIGURE 2 is a chart showing voltage changes at various points in the circuit of FIGURE 1, during a time delay period.

FIGURE 3 is a modified form of the circuit diagram of FIGURE 1 employing a second magnetic relay for fast recording action.

FIGURE 4 is an alternative circuit diagram wherein the transistor has a common base connection.

FIGURE 5 is an alternative circuit diagram wherein the transistor has a common emitter connection; and

FIGURE 6 is an alternative circuit for use in connection with a direct current power source.

In FIGURE 1, there is shown an alternating current BJMJZS Patented 69st. 27, I964 input transformer 28 :the secondary 22 of which is connected to a voltage multiplier circuit comprising oppositely connected diode rectifiers 24 and 26, and capacitors 28 and 30. Connected across the capacitors 28 and 30 is a series resistance capacitor circuit 31 comprising a capacitor 32 and a variable resistor 34, the latter being adapted to vary the time constant of the circuit.

A relay 36 which may be a conventional direct current relay having the usual winding 38, and in addition a secondary winding 56, is connected to the collector 42 of an NPN type junction transistor Q, the emitter 44 of which is connected to diodes 48 and 50, connected respectively to the mid-tap 68 of the resistance capacitor circuit 31, and to the common return 52 to the transformer secondary, and the common connection between capacitors 28 and Sit, the return 52 being grounded as at 54.

The relay Winding 38, which may be called the primary winding, is in transformer relation to the secondary winding 5e. Such secondary winding is connected to the transistor base 5'8 and ground 54-. One of the pairs of contacts as of the relay 36 may be employed in a hold in circuit, and a suitable current limiting resistor 64 in series therewith, may be provided, the hold in circuit, including contacts 60, being connected between the collector end of the relay Winding 38 and ground 54 which latter may be a point of reference potential. A diode 70 connected across the relay primary 3% may be provided to suppress voltage transients generated by the relay when the relay contacts open, in cases where the transient voltages might otherwise exceed the voltage rating of the transistor.

Prior to closing switch 6-5, all capacitors are uncharged. Upon closing switch 56, capacitor 28 is charged to the positive peak voltage with respect to ground of the transformer secondary during the first positive half cycle, and capacitor 3a is charged to the negative peak during the first negative half cycle. Thus during the first cycle of alternating current, the charging of capacitor 32 commences, the rate being controlled by resistor 34. The potential at 68 immediately commences to drop exponentially.

During the first half cycle, the voltage at 68 rises initially substantially to the positive peak voltage of capacitor 28. As capacitor 32 is charged through resistor 34, the voltage at 68 decreases exponentially towards the negative peak voltage of capacitor 30. During the time the voltage at 68 is positive, transistor Q is biased in cut off, since no emitter current can flow through either diode 48 or 553. The transistor is thus in common base connection as far as biasing is concerned so that only a small collector leakage current can flow through the collector circuit and relay coil 38. When the voltage at becomes slightly negative, diode 48 and emitter 44 become forward biased. As the emitter current of the transistor increases sufiiciently so that the gain of the transistor together with the relay coils 38 and 56 equals unity, the circuit becomes regenerative. The transistor is switched into saturation, and the voltage of capacitance 3. 5 is applied to the relay winding 38, inducing a voltage in the relay secondary 56. The secondary 56 is so connected as to apply a positive voltage to the transistor base 58, effective to maintain the transistor in saturation.

During the initial switching interval, the emitter current flows into capacitor 32. As soon as the emitter voltage equals the forward bias of the diode 50, the emitter current flows through diode Ell to ground and the voltage across capacitance 28 is applied to the relay coil 38. The length of time the transistor is maintained in saturation is thus independent of the size of capacitance 32, and of suflicient duration to actuate the relay and close the hold-in contacts es, and such other relay acareavss tuated contacts such as 61 employed to actuate a load, it being understood that capacitance 28 is sufficiently large to maintain the current through the relay above the holding level during a full cycle of the alternating current input.

The length of time that the transistor is held in saturation is determined by the characteristics of the transformer relay, and the gain of the transistor, and the length of time the transistor is held in saturation must be greater than the pull-in-time of the relay. This requirement determines the minimum operating voltage of the circuit. Once the relay pulls in, it is locked in by the current flowing through the hold in contacts 6t and resistor 64, the value of which is selected to provide the desired steady state current through the relay coil 38. Where the resistance of the relay coil 38 is sufficiently high, the resistance 64 may be eliminated.

When the relay has been activated, and the hold in circuit closed, opening switch 66 will reset the circuit.

The time delay of the circuit is approximately equal to 0.70 X the constant for the resistance 34 and capacitance 32, and the time delay constant may be readily varied by varying the resistor 34, which may be in the form of a potentiometer.

The maximum permissible value of resistance 34 is determined by the maximum emitter current required to trigger the transistor 46'. Such current is determined by the gain of the transistor, transformer relay combination at low signal levels. A typical value of this current may be 20 microamperes. The required current may be reduced by adding small capacitances (about .02 m.f.d.) in parallel with either diode 4% or 59. In practice the capacitance 39 may be eliminated, in which case capacitance 32 is charged only during the negative half cycle of the input voltage, and the time delay is increased about double. Diodes l8 and t may be silicon diodes with low leakage current, and diode 5t should preferably have a low junction capacity. The transistor may be germanium, provided the maximum ambient temperature does not exceed the transistor rating, but otherwise a silicon transistor should be employed.

In the circuit shown in FIGURE 3 provision is made for fail safe operation, and for rapid recycling. The circuit corresponds to that of FIGURE 1, except for the introduction of a second relay, the energizing coil 9%) of which is connected across the capacitance 3th, so as to be energized during the first negative half cycle of voltage applied, after closure of the switch es. When the coil is energized, contacts 92 actuated thereby, are opened, to permit charging of the capacitance 32. Other contacts closed by energization of the coil N, such as 94 may be those of a circuit to actuate a load.

When the transistor fires, relay contacts 64B are subsequently closed, and locked in by the discharge of capacitance 2% through the resistor 64 and relay primary 3%, at which time normally closed contacts 63 of relay 36 are opened, resulting in deenergizing coil 9%, and closing of switch @2, which immediately discharges capacitance 32, thus immediately preparing the circuit for a subsequent cycle of operation. If the circuit should fail, as for lack of power, or for any other reason, load actuating contacts such as 94 are opened.

Referring to FIGURE 2, there is shown typical operating voltage wave-forms for the circuit of FIGURE 1. In the diagram, the line voltage is applied by closing switch 66, at the time indicated at 67, whereupon the alternating current voltage at 76 comprises the usual wave form indicated at 76. Capacitance 23 promptly charges in accordance with the wave form 72, and capacitance 30 charges oppositely as is indicated by the wave form 74. Capacitance 32 commences to charge resulting in an exponential decrease in the potential at 63, as indicated by the wave form 68, and the potential at the transistor collector is represented by the curve 7 8. It will be seen that when the exponential curve 68 becomes negative,

after the passage of time, as indicated at es the transistor fires, reducing the potential 78 to a value appnoaching zero, and when the relay contacts as close shortly thereafter as indicated at 75, the potential further drops to a value, which may be zero, if resistor 64 be eliminated. By reason of the discharge of capacitance 23 momentarily resulting from the alternating current potential 76 being negative at the instant of firing, the curves 72 reflects a drop in potential as at 71, which is in part restored a half cycle later, tlus also has an effect upon the potential at 63, as at 73, but the transistor is already in saturation and is unaffected, so long as capacitor 28 is large enough to maintain the current flow through the relay coil above that required for actuation.

In FIGURE 4, there is shown a circuit similar to that of FIGURE 1, employing the transistor in a common base connection with the relay primary 38 connected to the collector 93 of transistor 46 and, wherein the relay secondary coil 56 is connected to the emitter of the transistor and through a diode 102 to the junction 164 between the time circuit including capacitor 32, and resistor 34. The hold-in circuit including contacts 60, and resistor 64 are also connected to the junction 104 through diode Th2, and the transistor base 106 is con! nected to the midconnection between capacitors 28 and Bill. The operation of this circuit is quite similar to that of FIGURE 1, except that the length of time that the transistor is saturated is determined by the value of capacitance 32, and a larger value would be required to actuate the relay.

IN FIGURE 5, a further variation is shown using the transistor 146 in common emitter connection. In this circuit, capacitor flit) is connected to capacitor 30 rather than 23, and thus the potential at 112 is initially at the negative peas, and is charged through resistor 114 towards a voltage equal to the positive peak of capacitance 28. When the voltage at 112 becomes slightly positive with respect to the potential at the emitter 116, the transistor is biased into conduction and is triggered, thus causing the relay to pull in. In this circuit, a resistor I18 con nected between the base 120, and capacitance is employed to provide a reverse bias on the transistor base to prevent thermal runaway. The transistor should have a low emitter to base leakage current, to keep the base reverse biased for the maximum value of collector cut off current at the maximum ambient temperature, and the upper limit of timing interval for a given value of capacitance lltl, is determined by the maximum collector cut oil current of the transistor. For this reason the circuit is not adapted to germanium transistors operating in high ambient temperatures. At low ambient temperatures with silicon transistors having a low emitter to base leakage current, the resistor 118 may be eliminated from the circuit, and the connection between the secondary 56 and the base 126 may be direct, eliminating the diode 122.

In FIGURE 6, a circuit for use with a direct current supply is shown. Such circuit comprises a source of direct current controlled by power switch 166. The primary 38 of the relay 36 is connected through a diode to the resistance capacitor time delay circuit comprising capacitance I52, and resistor 154, which are in turn connected to ground as at 156. Resistors 158 and 16% provide a mid potential at 162 which is connected through the relay secondary 56 to the transistor base 164. The transistor collector 163 is connected to the primary 38, and the emiter 17% is connected through a diode 172 to the junction 174 betwen capacitance 152 and resistor 154. A hold-in circuit comprising relay contacts 60, and a current limiting resistor 64 is provided. Capacitance 176 connected across resistor is employed to increase the gain of the circuit and to improve firing resistivity. Operation of the circuit will be apparent from the above. When the voltage at junction 174 decreases from its initial positive potential of the input, as capacitance 152 charges, the potential at the junction become slightly negative in respect to the potential applied to the base, and the base to emitter junction is forward biased, and the transistor fires causing the relay to pull in. The instant of firing results in increased current flow in primary 38, inducing a secondary voltage in winding 56, which maintains tran sistor saturation.

While several embodiments of the invention have been iluustrated and described, it is to be understood that the invention is not limited thereto. As various changes in the circuitry may be made without departing from the spirit of the invention, as will be apparent to those skilled in the art, reference will be had to the appended claims for definition of the limits of the invention.

What is claimed is:

1. A time delay relay circuit comprising an electro-magnetic relay having a primary relay actuating coil and a secondary winding in transformer relation thereto, a signal source, a resistor capacitor time delay circuit in circuit with said signal source and having a junction, the potential of which varies exponentially, means for establishing a reference potential within the range of variation of said junction potential, a transistor having its collector, and one of its base and emitter connections in series with said coil and across said capacitor, and having the other of its base and emitter connected through said winding to said reference potential means.

2. A time delay circuit comprising a signal source, a voltage rectifier and doubler circuit connected to said source including means for establishing a reference potential, a resistor capacitor time delay circuit connected across the output of said doubler circuit and having a junction the potential of which varies through the reference potential with the charging of the capacitor, an electro magnetic relay having a primary relay actuating coil and a secondary winding in transformer relation thereto a transistor having its collector and one of its base and emitter connections connected in series with said coil across the capacitor of said time delay circuit, and the other of its emitter and base connection connected through said winding to said reference potential.

3. A time delay circuit comprising a signal source, a

voltage rectifier and doubler circuit connected to said source including means for establishing a reference potential, a resistor capacitor time delay circuit connected across the output of said doubler circuit and having a junction the potential of which varies through the reference potential with the charging of the capacitor, an electro magnetic relay having a primary relay actuating coil and a secondary winding in transformer relation thereto, a transistor having its collector and one of its base and emitter connections connected in series with said coil across the capacitor of said time delay circuit, and the other of its emitter and base connection connected through said winding to said reference potential, and hold in contacts closed by said relay connected between the collector and said reference potential means.

4. A time delay circuit comprising a signal source, a voltage rectifier and doubler circuit connected to said source including means for establishing a reference potential, a resistor capacitor time delay circuit connected across the output of said doubler circuit and having a junction the potential of which varies through the reference potential with the charging of the capacitor, an electro magnetic relay having a primary relay actuating coil and a secondary winding in transformer relation thereto, a transistor having its collector and one of its base and emitter connections connected in series with said coil across the capacitor of said time delay circuit, and the other of its emitter and base connection connected through said winding to said reference potential, a second relay having normally closed contacts across said time delay capacitance acting in response to said signal source to open said contacts, and normally closed contacts in circuit with said second relay opened by actuation of said first relay.

References Cited in the file of this patent UNITED STATES PATENTS 2,981,898 St. John Apr. 25, 1961 3,010,053 Schubert Nov. 21, 1961 3,018,419 Bonn Jan. 23, 1962 

1. A TIME DELAY RELAY CIRCUIT COMPRISING AN ELECTRO-MAGNETIC RELAY HAVING A PRIMARY RELAY ACTUATING COIL AND A SECONDARY WINDING IN TRANSFORMER RELATION THERETO, A SIGNAL SOURCE, A RESISTOR CAPACITOR TIME DELAY CIRCUIT IN CIRCUIT WITH SAID SIGNAL SOURCE AND HAVING A JUNCTION, THE POTENTIAL OF WHICH VARIES EXPONENTIALLY, MEANS FOR ESTABLISHING A REFERENCE POTENTIAL WITHIN THE RANGE OF VARIATION OF SAID JUNCTION POTENTIAL, A TRANSISTOR HAVING ITS COLLECTOR, AND ONE OF ITS BASE AND EMITTER CONNECTIONS IN SERIES WITH SAID COIL AND ACROSS SAID CAPACITOR, AND HAVING THE OTHER OF ITS BASE AND EMITTER CONNECTED THROUGH SAID WINDING TO SAID REFERENCE POTENTIAL MEANS. 